As a resin pipe joint of this kind, a tube joint disclosed in Patent Literature 1 is known. Namely, the tube joint is structured in the following manner. A synthetic resin-made tube 1 is forcedly pressed onto an inner cylinder portion 5 of a joint body 4, or, as shown in FIG. 2 of Patent Literature 1, a tube end portion 2 is previously flared and then fitted to the inner cylinder portion 5. Then, a union nut 6 which is previously fitted to the tube is screwed with the joint body, and forcedly moved in the axial direction of the joint body 4 by performing a fastening operation, whereby a flaring base portion 2a of the tube 1 is strongly pressed in the axial direction by an edge portion 6a to seal between the tube 1 and the inner cylinder portion 5.
As a structure similar to the above-described structure, a structure disclosed in FIGS. 8 and 9 of Patent Literature 2, and a resin pipe joint disclosed in FIG. 6 of Patent Literature 3 are known. As shown in these figures, a joint structure in which the tip end of a tube is flared, externally fitted to a joint body, and fastened by a nut has an advantage that a good sealing function is obtained although a pipe joint is economically configured by a small number (two) of components, i.e., the joint body and a union nut, as compared with a structure disclosed in FIG. 5 of Patent Literature 2, FIG. 5 of Patent Literature 3, and the like, i.e., a pipe joint having a three-component structure in which an end of a tube that is flared and externally fitted to an inner ring that is a dedicated component is fitted into a tubular receiving port of a joint body, and fastened by a union nut.
In a conventional resin pipe joint which is configured by two components as described above, however, an end of a tube is flared and firmly fitted, and a flaring base portion is fastened by a union nut, and, probably because the fastening is performed in order to attain a sealing function, there is a tendency that the joint is relatively weak against a force of pulling the tube out of a joint body. A pulling movement itself of a tube is problematic. There is a further problem in that this movement causes also a seal point due to the pressing by an edge portion to be shifted, and the sealing property is adversely influenced. In the case where, in order to handle a high-temperature fluid of 100° C. or higher, a resin pipe joint is formed by a resin material having a large coefficient of expansion such as a fluorine resin, particularly, these problems become more noticeable.
As disclosed in Patent Literature 4, therefore, it is known that a resin pipe joint which exerts not only a sealing function but also a resistance against pulling of a tube is obtained by disposing pulling resistant means having a structure in which a C-like split ring is interposed between a flared portion of the tube and a union nut in a state where the ring is fitted into a peripheral groove of the tube flared portion. In the resin pipe joint disclosed in Patent Literature 4, however, preprocessing of previously forming the peripheral groove in the tube flared portion is necessary, and the number of components is increased to three. Therefore, there arises a new problem in that the economical advantage which is originally provided in such a resin pipe joint is impaired. In order that a resin pipe joint configured by two components or a joint body and a union nut is formed so as to have a high resistance against pulling without causing the new problem, consequently, there remains room for further improvement.